Image processor, image processing method, and computer program

Abstract

Disclosed herein is an image processor including: a depth image acquisition portion adapted to acquire a depth image for an image frame making up the movie, the depth image representing, as a pixel value on an image plane, a subject distance from an imaging device; an edge extraction portion adapted to generate an edge image for the image frame and identify a picture area of a tracked target in the depth image on the basis of an outline of the tracked target represented by tracking results for the image frame at a previous time so as to extract an edge in an area limited on the basis of the picture area; and a tracking section adapted to compare the extracted edge against an outline candidate for the tracked target to find a likelihood so as to estimate the outline of the tracked target and output the outline as tracking results.

What is claimed is: 
     
       1. An image processing method for an image processor to track a first tracked target and a second tracked target in a movie, the first tracked target located at a first z-distance z1 and the second tracked target located at a second z-distance z2 at least a z-distance z3 from z1, the image processing method comprising:
 a) calculating a depth image from an image frame making up a movie at time t, the depth image representing, as a pixel value on an image plane, a unique subject distance from an imaging device, 
 wherein the depth image is calculated for an entirety of the image frame; 
 b) acquiring a first tracking result for the first tracked target and a second tracking result for the second tracked target at time t−1, 
 c) determining a first processing area for the first tracked target and a second processing area for the second tracked target, 
 wherein the first processing area and the second processing area are determined based on a basis of movable ranges of the first tracked target and the second tracked target, respectively, 
 wherein the first z-distance and the second z-distance are used to adjust the movable ranges, 
 d) extracting a first picture area for the first tracked target from the image frame at time t by:
 fitting the first tracking result at time t−1 to the depth image: 
 calculating an average z-distance Zt for all pixels within an area bounded by the first tracking result; and 
 extracting all pixels in the image frame which have values within a range of Zt−ΔZ<z1<Zt+ΔZ in the depth image to form the first picture area, 
 wherein ΔZ<z3; 
 
 e) extracting a second picture area for the second tracked target from the image frame at time t by:
 fitting the second tracking result at time t−1 to the depth image: 
 calculating an average z-distance Zw for all pixels within an area bounded by the second tracking result; and 
 extracting all pixels in the image frame which have values within a range of Zw−ΔZ<z2<Zw+ΔZ in the depth image to form the second picture area; 
 
 f) generating a third tracking result for the first tracked target at time t using the first picture area; 
 g) generating a fourth tracking result for the second tracked target at time t using the second picture area; and 
 h) repeating steps a)-g) for an image frame at time t+1 to track the first tracked target and the second tracked target in the movie. 
 
     
     
       2. The method of  claim 1 , wherein the wherein step c) further includes extracting a foreground area from the image frame using a background image prepared in advance. 
     
     
       3. The method of  claim 1 , wherein the image frame is subjected to gray level reduction prior to steps d) and e). 
     
     
       4. An image processing method for an image processor to track a tracked target in a movie, the image processing method comprising:
 a) calculating a depth image from an image frame making up a movie at time t, the depth image representing, as a pixel value on an image plane, a unique subject distance from an imaging device, 
 wherein the depth image is calculated for an entirety of the image frame; 
 b) acquiring a tracking result for the tracked target at time t−1, 
 c) determining a processing area for the first tracked target, 
 wherein the processing area is determined based on a movable range of the tracked target, 
 wherein a z-distance z1 of the tracked target is used to adjust the movable range, 
 d) extracting a picture area for the tracked target from the image frame at time t by:
 fitting the tracking result at time t−1 to the depth image: 
 calculating an average z-distance Zt for all pixels within an area bounded by the tracking result; 
 and extracting all pixels in the image frame which have values within a range of Zt−ΔZ<z1<Zt+ΔZ in the depth image to form the picture area; 
 
 e) generating a tracking result for time using the picture area; 
 f) repeating steps a)-e) for an image frame at time t+1 to track the tracked target in the movie.